The present invention relates generally to the art of hydraulic control devices and more specifically relates to a pressure modulation valve for automatically controlling pressure buildup in a fluid pressure consuming unit.
When actuating many hydraulic devices it is desirable to gradually bring the device up to full pressure rather than actuating the device with a pressure surge. An example of such a device would be a hydraulically applied clutch wherein it is desirable to gradually engage the clutch to avoid shock loads on the driven parts. With other hydraulic devices it is desirable to initially provide a large volume of flow to initially fill the device and then gradually bring the device up to full pressure. In the past many proposals have been made to provide modulating valves which permit the pressurization of hydraulic devices with the desired pressure-flow characteristics. All such devices have at least one characteristic in common, that is, they have a movable valve member or slide which is responsive to an increase in fluid pressure to gradually open or close a fluid passage.
Some prior valves initially provided full fluid flow to the devices and, when a certain pressure was reached, exhausted a portion of the fluid provided to the valve to reservoir and gradually cut off the flow to the reservoir as pressure built up. Such devices were not only complicated, but were subject to fluttering of the movable valve member. Other prior art valves required an extra movable member which functioned as an accumulator in order to provide the desired pressure buildup characteristics. These valves were again complicated and relatively expensive.